JPH0483707A - Aluminum nitride power and production thereof - Google Patents

Abstract

PURPOSE:To obtain fine aluminum nitride powder with hardly any impurities in a short time by adding a nitrogen-containing substance to a mixture of alumina (hydrate) with carbon, carrying out multistage heat treatment and subjecting the aforementioned mixture to reductive nitriding reaction in a nitrogen atmosphere. CONSTITUTION:A nitrogen compound is added to a mixture of alumina and/or alumina hydrate with carbon. The resultant mixture is then subjected to multistage heat treatment within mutually different temperature ranges to carry out reductive nitriding reaction in a nitrogen atmosphere. The first heat treatment and the second heat treatment performed within a higher temperature range than that in the first heat treatment are carried out as the aforementioned reductive nitriding reaction step. Thereby, 2 powder having >=3m<2>/g specific surface area (measured by the BET method) and a composition composed of <=0.1wt.% carbon content and the remainder of aluminum nitride is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to aluminum nitride powder and a method for producing the same.

[Prior Art] Aluminum nitride is generally known as a material with high thermal conductivity and electrical insulation, or unless stable and highly pure aluminum nitride powder is used, aluminum nitride has its own high thermal conductivity. Sintered bodies were difficult to obtain. but.

With recent advances in aluminum nitride manufacturing technology and sintering technology, sintered bodies with high thermal conductivity of 200 W/sK or more have been developed.

Examples of methods for producing this type of aluminum nitride powder include a direct nitriding method in which aluminum powder is directly nitrided, and a reductive nitriding method in which alumina powder is reduced and nitrided. The former direct nitriding method requires a pulverization step to pulverize the aluminum nitride powder, and there are problems such as the contamination of impurities during this step.

In fact, industrially, the latter method, the alumina reduction nitridation method, is the mainstream.

On the other hand, in the alumina reduction nitriding method, a mixture of alumina or alumina hydrate and carbon is added with N2 as a nitrogen source. A method has been proposed in which aluminum nitride powder is synthesized by contacting with a gas containing NH or N2-NH as an atmospheric gas and holding it at a high temperature, generally 1250°C or higher, for 2 hours or more, preferably 4 to 5 hours or more. (Unexamined Japanese Patent Publication 1986
225506, JP 63-182207, JP 63-103806) [Problems to be Solved by the Invention] However, in the above-mentioned reductive nitriding method.

For example, since the mixture is processed at a relatively low temperature of about 1250°C, it has the disadvantage that fine aluminum nitride powder cannot be obtained unless it is held for 2 hours or more, preferably 4 to 5 hours or more. be.

Therefore, one technical problem of the present invention is fine particles.

Another object of the present invention is to provide aluminum nitride powder with low impurities and a method for rationally producing it in an extremely short period of time.

[Means for solving the problem] According to the present invention, the specific surface area (BET method) is 3.0 m2/
g or more, an aluminum nitride powder is obtained which is characterized in that carbon is less than 0.10 t % and the balance is substantially aluminum nitride.

According to the present invention, a method for producing aluminum nitride by heating and reacting a mixture of at least one of alumina and alumina hydrate with carbon in an atmosphere containing nitrogen includes the step of adding a nitrogen-containing substance to the mixture. , a step of subjecting the mixture to which the nitrogen-containing substance has been added to a reduction-nitridation reaction through multi-stage heat treatment in mutually different temperature ranges.

The step of causing a reduction-nitridation reaction through the multi-stage heat treatment includes a first heat treatment and a second heat treatment in a temperature range equal to or higher than the first heat treatment.
There is obtained a method for producing aluminum nitride powder, characterized in that it includes a heat treatment.

In the present invention, the method for producing aluminum nitride powder preferably includes a step of performing heat treatment in an oxidizing atmosphere within a temperature range of 600° C. to 750° C. after the multistage heat treatment step.

[Function] In the present invention, by performing one synthesis in a short time, grain growth of aluminum nitride powder can be suppressed and fine grained aluminum nitride powder can be synthesized. Moreover, as a result, the amount of impurity carbon in this aluminum nitride powder can be extremely small.

[Example code] Examples of the present invention will be described below.

Example 1 Alumina with a purity of 99.6%2 and a center particle size of 0.4 μm and carbon black containing 0.4% ash at a molar ratio of C/Al□
0. −6.0, and the molar ratio of industrial urea as nitrogen source to alumina (C0(NH2) 2 + /A
I203-0. They were mixed at a ratio of 29. At that time, 90 wt % of isopropyl alcohol was added as a binder based on the total amount of alumina and carbon, and 2 wt % of polyethylene glycol was added as a thickener. After thoroughly mixing these, use an Oshida molding machine to form a mold with a diameter of 1 arm and a length of 2 to 7 mm.
It was granulated and molded into cylindrical pellets with a diameter of mm. After drying such a pellet, it was continuously heat-treated in a one-rotary furnace under two-stage treatment conditions: a first heat treatment and a second heat treatment.

At this time, the raw material is 0. Input 5kg/hr.

N2 gas was supplied as an atmospheric gas in a countercurrent manner.

In the rotary furnace, the first heat treatment is performed by supplying N2 [801
The pellets were fed for 7 minutes, and the pellets were kept in a temperature range of 1655°C for 10 minutes.The second heat treatment was carried out with N
2 was supplied at a rate of 50 g/min, and the temperature was maintained at 1950° C. for 10 minutes. Carbon remaining in the synthesized aluminum nitride pellet was removed by heat treatment at 700° C. for 3 hours in the air. The characteristic values of the obtained aluminum nitride powder are
Shown in the table. From this, the obtained aluminum nitride has a carbon content of 0.06 wt% and an oxygen content of 1.34 wt%.
wt%, specific surface area (BET method) = 3, 39 yr2/
g, the particles were fine and contained few impurities.

Example 2 In the same manner as in Example 1, raw material pellets were prepared and continuously treated in a two-rotary furnace.

The first heat treatment in the rotary furnace was performed while N2 was supplied at a rate of 80 p/min and the pellet was held in a temperature range of 1655° C. for 10 minutes.

The second heat treatment was carried out while the pellet was kept in a temperature range of 1950° C. for 30 minutes with a supply of N2 of 80 g/min. Carbon remaining in the synthesized aluminum nitride pellet was removed in the same manner as in Example 1. The properties of the obtained aluminum nitride powder are shown in Table 1 together with Example 1. The aluminum nitride powder obtained from this is carbon.

Although the oxygen content is low, the specific surface area (BET method) -2, 6
The grains were slightly grown at 4ta2/g.

Example 3 Raw material pellets were prepared in the same manner as in Example 1 and continuously treated in a one-rotary furnace.

In the first heat treatment in the rotary furnace, N2 was supplied in an amount of 80 g/
The pellet was kept in a temperature range of 1620°C for 10 minutes, and the second heat treatment was carried out in a temperature range of 1950°C with N2 supplied at a rate of 50g/min. 1 by holding the pellet for 10 minutes.

Carbon remaining in the synthesized aluminum nitride pellet was removed in the same manner as in Examples 1 and 2.

Table 1 shows the properties of the obtained aluminum nitride powder.

The aluminum nitride powder obtained from Table 1 was fine with a specific surface area (BET method) of -3.07 ta2/g, but the carbon content was somewhat high at 0.10 wt%.

Example 4 Raw material pellets were prepared in the same manner as in Example 1 and continuously treated in a two-rotary furnace. In this case, the first heat treatment was carried out by supplying N2 at a rate of 80 I/min and holding the pellet in a temperature range maintained at 1750° C. for 10 minutes, and in the second heat treatment.

This was done by supplying N2 at a rate of 50 g/min and holding the pellet in a temperature range maintained at 1950° C. for 10 minutes. Carbon remaining in the synthesized aluminum nitride pellet was removed in the same manner as in Example 1. The properties of the obtained aluminum nitride powder are shown in Table 1. The aluminum nitride powder thus obtained had a considerably high carbon content of 0.15 wt%.

In order to explain the present invention in detail, a comparison of characteristics between Examples 1 to 4 and a comparative example was made. Before explaining the comparison, Comparative Examples 1 and 2 will be explained.

Comparative Example 1 Aluminum nitride was produced in the same manner as in Example 4, except that the second heat treatment was not performed.

The results are shown in Table 1. The obtained powder had a carbon content of 0.09%, a low nitrogen content of 26.55 wt%, and an extremely high oxygen content of 12.32 vt%.

Comparative Example 2 Aluminum nitride was produced in the same manner as in Example 3, except that the second heat treatment was not performed.

The results are shown in Table 1. The obtained powder has an extremely low nitrogen content of 20.43 νt% and an oxygen content of 2.
It was extremely high at 0.48%.

Comparative Example 3 Aluminum nitride was produced in the same manner as in Example 1, except that the second heat treatment was not performed.

The results are shown in Table 1. The obtained powder had a carbon content of 0.28%, a low nitrogen content of 30.94 wt%, and a high oxygen content of 2.99 wt%.

In the embodiments of the present invention described above, the alumina powder, which is one of the raw materials for the aluminum nitride powder, includes Fe, St, which has a negative effect on the thermal conductivity of the aluminum nitride sintered body,
It is preferable to use fine particles with a high purity and a particle size of 2 μm or less, with a small amount of elements such as Mg.

Further, as the other raw material carbon, acetylene black, which is fine and has good reactivity, is preferable.

In addition, in the present invention, the blending ratio of these raw materials is the molar ratio C/p of alumina and carbon, 120*-4.
~6 is preferable; if there is little carbon, 1 reactivity will be poor, and conversely, if there is a lot of carbon, the process of removing excess carbon after aluminum nitride synthesis will be difficult, and not only will the cost be high, but also there may be a large amount of impurities. There is sex. On the other hand, in this example, urea was used as the nitrogen-containing substance, but inorganic nitrogen (ammonium sulfate) was used in addition to urea.

ammonium chloride, ammonium nitrate, etc.), and organic nitrogen (lime nitrogen, ammoniated peat, etc.). However, impurities, nitrogen content 1 workability.

Considering economic efficiency, urea (CO(NH2) 2 ) is preferable. This urea is often used as a fertilizer.
Not only is it relatively inexpensive, but it is also highly pure. This nitrogen-containing substance accelerates the reductive nitriding reaction by being added to the raw material. This nitrogen-containing substance is urea (Co (NH
2) When adding 2), the amount added is preferably Co(NH2)2/A1203-0.15 or more in molar ratio with alumina. This is because when the molar ratio is less than 0.15, the effect is weak.

In the examples of the present invention, polyethylene glycol was used as a thickener and isopropyl alcohol was used as a binder as raw materials, but it is also possible to use water or ethanol as other binders.

In the embodiments of the present invention, the atmosphere for the reduction-nitridation reaction is as follows.

Although N2 is used, NH3, N2 H2, N2N
Any atmosphere containing nitrogen such as H, etc. can be used.

In addition, in the example of the present invention, the first heat treatment and the second heat treatment were used to perform one synthesis reaction, but the multi-stage heat treatment includes at least the first heat treatment and the second heat treatment. It is sufficient if it is included in the process in this order. This first heat treatment is preferably performed at a temperature of 1700° C. or lower for 10 minutes.

Further, after roasting this, it is necessary to reduce the carbon content to 0.20% by weight or less. This is because when the temperature in the first heat treatment is raised to 1,700°C or higher, a reaction occurs rapidly, and carbon becomes solid solution in the produced aluminum nitride, which cannot be removed by roasting in the subsequent process. Also, in the first heat treatment, the nitrogen content is 20.
If it is less than 0% by weight, there is a lot of unreacted alumina, so 18
Carbon is dissolved in aluminum nitride produced in the second heat treatment performed at 00° C. or higher, making it difficult to remove.

Furthermore, in a second heat treatment following the first heat treatment.

It is necessary to set the synthesis temperature to 1800°C or higher and hold it for 10 minutes or more. In the second heat treatment, the higher the temperature, the lower the oxygen content.

A high temperature of 1900° C. or higher is preferable, but holding for 10 to 30 minutes is appropriate because one grain will grow if held for 30 minutes or more. After synthesizing aluminum nitride by the reductive nitriding method, it is appropriate to remove excess carbon by heat treatment at a temperature of 680 to 750° C. for 2 to 4 hours in an oxidizing atmosphere. This is because if the temperature is below 680"C, it takes a long time to remove carbon, and if the temperature is above 750"C, rapid oxidation of aluminum nitride occurs.

In the embodiments of the present invention described above, the obtained aluminum nitride powder has a low content of oxygen and carbon, which cause lattice defects to occur in the crystals of the sintered body and thereby reduce thermal conductivity.

It is useful as a raw material for highly thermally conductive sintered bodies.

Although the heat treatment was carried out using a 1-rotary furnace in the examples of the present invention, it is clear that the synthesis reaction can be carried out without using a 9-rotary furnace.

Margin below [Effects of the invention As explained above, according to the present invention, in the past,
By alumina reduction method with carbon.

In order to obtain fine grained aluminum nitride powder, a synthesis time of 2 hours or more, preferably 4 to 5 hours or more was required, but the present invention can produce fine grains in an unprecedentedly extremely short time of less than 1 hour, and It is possible to provide aluminum nitride powder with few impurities and a method for reasonably obtaining the powder.

Procedural amendment (voluntary) August 1990 - 73rd

Claims (1)

[Claims] 1. Aluminum nitride having a specific surface area (BET method) of 3.0 m^2/g or more, carbon content of 0.10 wt% or less, and the remainder substantially consisting of aluminum nitride. powder. 2. A method for producing aluminum nitride by heating and reacting a mixture of at least one of alumina and alumina hydrate with carbon in an atmosphere containing nitrogen, comprising: adding a nitrogen-containing substance to the mixture; the mixture to which the compound has been added is subjected to a reduction-nitridation reaction through multi-stage heat treatment in mutually different temperature ranges, and the step of causing the reduction-nitridation reaction through the multi-stage heat treatment is a first step.
A method for producing aluminum nitride powder, comprising: a heat treatment; and a second heat treatment performed in a temperature range equal to or higher than the first heat treatment.